Hi. I am using MAAS Version 1.8.3 (+bzr4053). I am facing MAAS failed to commission issue.  
->from /var/log/maas/

maas.log
========
Jul 21 16:01:30 maas maas.node: [INFO] slvae1: Status transition from NEW to COMMISSIONING
Jul 21 16:01:30 maas maas.dns: [INFO] Generating new DNS zone file for maas
Jul 21 16:01:30 maas maas.dns: [INFO] Generating new DNS zone file for 10.168.192.in-addr.arpa
Jul 21 16:01:31 maas maas.power: [INFO] Changing power state (on) of node: slvae1 (node-4988196e-4f2e-11e6-b450-0800272733e3)
Jul 21 16:01:31 maas maas.node: [INFO] slvae1: Commissioning started
Jul 21 16:01:32 maas maas.power: [INFO] Changed power state (on) of node: slvae1 (node-4988196e-4f2e-11e6-b450-0800272733e3)
Jul 21 16:02:35 maas maas.node: [INFO] slave2: Status transition from NEW to COMMISSIONING
Jul 21 16:02:35 maas maas.dns: [INFO] Generating new DNS zone file for maas
Jul 21 16:02:35 maas maas.dns: [INFO] Generating new DNS zone file for 10.168.192.in-addr.arpa
Jul 21 16:02:35 maas maas.power: [INFO] Changing power state (on) of node: slave2 (node-703837f6-4f2e-11e6-b450-0800272733e3)
Jul 21 16:02:35 maas maas.node: [INFO] slave2: Commissioning started
Jul 21 16:02:37 maas maas.power: [INFO] Changed power state (on) of node: slave2 (node-703837f6-4f2e-11e6-b450-0800272733e3)
Jul 21 16:04:11 maas maas.macaddress: [INFO] slvae1 00:a0:d1:ea:fb:d9 linked to cluster interface enp0s3
Jul 21 16:04:35 maas maas.lease_upload_service: [INFO] Uploading 1 DHCP leases to region controller.
Jul 21 16:04:37 maas maas.macaddress: [INFO] slave2 00:a0:d1:ea:90:95 linked to cluster interface enp0s3
Jul 21 16:05:35 maas maas.lease_upload_service: [INFO] Uploading 2 DHCP leases to region controller.
Jul 21 16:19:35 maas maas.import-images: [INFO] Started importing boot images.
Jul 21 16:19:36 maas maas.import-images: [INFO] Finished importing boot images, the region does not have any new images.
Jul 21 16:21:31 maas maas.node: [INFO] slvae1: Status transition from COMMISSIONING to FAILED_COMMISSIONING
Jul 21 16:21:31 maas maas.node: [ERROR] slvae1: Marking node failed: Node operation 'Commissioning' timed out after 0:20:00.
Jul 21 16:21:51 maas maas.node_query: [INFO] slvae1: Power is on.
Jul 21 16:22:35 maas maas.node: [INFO] slave2: Status transition from COMMISSIONING to FAILED_COMMISSIONING
Jul 21 16:22:35 maas maas.node: [ERROR] slave2: Marking node failed: Node operation 'Commissioning' timed out after 0:20:00.
Jul 21 16:22:56 maas maas.node_query: [INFO] slave2: Power is on.


vedams@maas:~$ sudo tail -f regiond.log
[sudo] password for vedams:
2016-07-21 16:27:05 [-] 127.0.0.1 - - [21/Jul/2016:10:57:05 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:27:35 [-] 127.0.0.1 - - [21/Jul/2016:10:57:35 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:28:05 [-] 127.0.0.1 - - [21/Jul/2016:10:58:05 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:28:35 [-] 127.0.0.1 - - [21/Jul/2016:10:58:35 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:29:05 [-] 127.0.0.1 - - [21/Jul/2016:10:59:05 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:29:35 [-] 127.0.0.1 - - [21/Jul/2016:10:59:35 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:30:05 [-] 127.0.0.1 - - [21/Jul/2016:11:00:05 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:30:35 [-] 127.0.0.1 - - [21/Jul/2016:11:00:35 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:31:05 [-] 127.0.0.1 - - [21/Jul/2016:11:01:05 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"
2016-07-21 16:31:35 [-] 127.0.0.1 - - [21/Jul/2016:11:01:35 +0000] "GET /MAAS/rpc/ HTTP/1.1" 200 276 "-" "provisioningserver.rpc.clusterservice.ClusterClientService"

vedams@maas:~$ sudo tail -f clusterd.log
2016-07-21 16:04:41+0530 [-] Stopping protocol <tftp.bootstrap.RemoteOriginReadSession instance at 0x7f46084915f0>
2016-07-21 16:04:41+0530 [TFTP (UDP)] Datagram received from ('192.168.10.5', 49162): <RRQDatagram(filename=ubuntu/amd64/generic/xenial/release/boot-initrd, mode=octet, options={'tsize': '0', 'blksize': '1408'})>
2016-07-21 16:04:41+0530 [-] RemoteOriginReadSession starting on 58429
2016-07-21 16:04:41+0530 [-] Starting protocol <tftp.bootstrap.RemoteOriginReadSession instance at 0x7f46084e76c8>
2016-07-21 16:04:43+0530 [-] Timed during option negotiation process
2016-07-21 16:04:43+0530 [-] (UDP Port 33049 Closed)
2016-07-21 16:04:43+0530 [-] Stopping protocol <tftp.bootstrap.RemoteOriginReadSession instance at 0x7f46084a1488>
2016-07-21 16:05:13+0530 [RemoteOriginReadSession (UDP)] Final ACK received, transfer successful
2016-07-21 16:05:13+0530 [-] (UDP Port 58429 Closed)
2016-07-21 16:05:13+0530 [-] Stopping protocol <tftp.bootstrap.RemoteOriginReadSession instance at 0x7f46084e76c8>